(1) Field of the Invention
This invention relates to gas enrichment utilizing pressure swing adsorption techniques, and more particularly to an improved pressure swing adsorption process and apparatus including gaseous diffusion barriers for gas enrichment.
(2) Description of the Prior Art
The use of adsorption techniques to separate a gaseous component from a gaseous stream initially was developed for the removal of carbon dioxide and water from air. The principles of gas adsorption were further refined to processes for gas enrichment of hydrogen, helium, argon, carbon monoxide, carbon dioxide, nitrous oxide, oxygen and nitrogen. Still further refinements using at least two adsorption vessels in a cycling pressurized relationship have resulted in an adsorption technique for gas enrichment commonly referred to as pressure swing adsorption (PSA).
A conventional PSA process for enriching a gas, such as nitrogen from air, employs at least two adsorption beds filled with carbon molecular sieve material, each subjected to two or more, generally four distinct processing steps in each cycle. In a first step of the cycle, one adsorption bed is pressurized with concomitant nitrogen production while the other bed is regenerated, such as by venting. The adsorption bed may also be regenerated with countercurrent flow of product-quality gas (referred to as "purge"). In a second step, sometimes referred to as pressure equalization, the adsorption beds are brought to an intermediate pressure by interconnection of the adsorption beds. In a third step of the cycle, the first adsorption bed is regenerated following the procedure used for the second bed while the second bed is put into production. The last step of the cycle is pressure equalization between the beds. During such pressure swings, pressure conditions in the adsorption beds vary between about 15 psia to 120 psig in a process employing carbon molecular sieves for nitrogen production and somewhat lower pressure ranges in processes employing crystalline zeolites for producing oxygen.
The use of an oxygen separation membrane in a pressure swing adsorption process is disclosed in Japanese Patent Application No. Sho 51(1982)-31576, filed Feb. 27, 1982 wherein oxygen is produced by PSA techniques in adsorption columns filled with zeolite particles and wherein during the purge cycle of each adsorption column an oxygen purge gas is passed therethrough. The oxygen purge gas is obtained as a gaseous permeate stream from a gas separation membrane into which an enriched oxygen stream is introduced during a production cycle of each of the adsorption columns.